This invention relates to a method of operating an internal combustion engine. More particularly, this invention relates to a method of operating an internal combustion engine that includes lubricating the high wear areas of the engine (e.g., wear interfaces or contacts of valve train components such as cam lobes, tappets, followers, valve tips, rocker arms, rocker arm mechanisms, and the like) with a solid film lubricant, and lubricating the entire engine, including the high wear areas, using a low-phosphorus or phosphorus-free lubricating oil composition. In one embodiment, this invention also relates to a method of operating the foregoing engine that provides an increase in the time intervals required between oil changes.
A problem associated with internal combustion engines equipped with exhaust gas aftertreatment devices (e.g., catalytic converters, particulate traps, etc.) is that the lubricating oils for such engines are used in both the crankcase as well as in high wear areas such as the valve train. Because these oils are used in high wear areas they typically contain extreme pressure (EP) agents which typically contain metal and phosphorus (e.g., zinc dialkyl dithiophosphate) in order to be effective. During the operation of the engine these EP agents decompose and the resulting decomposition products eventually enter the aftertreatment device and often contribute to damaging the device. The problem therefore is to provide a lubricant system that adequately addresses the antiwear protection needs of the high wear areas of the engine and yet avoids damage to the exhaust gas aftertreatment device.
Another problem associated with conventional internal combustion engines is that blow-by exhaust gases generated in the crankcase of the engine typically come into contact with the valve train system. Blow-by exhaust gases have been found to be a primary factor affecting valve train wear. The problem therefore is to provide a lubricant system that avoids or reduces valve train wear.
Another problem associated with conventional internal combustion engines is that the time interval required between oil changes typically is less than the time interval required for other service items such as air filter replacements, coolant changes, brake replacements, and the like. Oil changes are viewed as one of the most aggravating and, in some cases, most costly maintenance aspects of vehicle ownership. Traditionally, oil change intervals have been extended by base stock and additive upgrades. Since the 1920s, for example, the extensions have been about 15xc3x97 or greater. Regardless of this progress, the time intervals required between oil changes continue to lag behind the time intervals required for other service items. The problem therefore is to improve the lubricant technology for these engines so that the time intervals between oil changes can be extended to coincide with other service intervals.
The present invention provides a solution to each of these problems. With the present invention low-phosphorus or phosphorus-free lubricating oil compositions characterized by a low-level or absence of EP agents containing metal and phosphorus are used and as a result the exhaust gas aftertreatment device is protected from harmful exposure to the decomposition products of these agents. The use of these low-phosphorus or phosphorus-free lubricating oil compositions in all parts of the engine, including the high wear areas of the engine, is possible due to the use of solid film lubricants in the high wear areas. In accordance with one embodiment of the invention, the required oil change intervals for these engines are extended due to the fact that used engine oil is continuously or periodically removed from the engine and replaced with new oil.
The use of solid film lubricants is known. U.S. Pat. No. 5,482,637 discloses the use of thin anti-friction films comprised of at least two solid lubricants selected from graphite, MoS2, and BN. U.S. Pat. No. 5,358,753 discloses the use of an anti-friction film comprised of graphite and MoS2. International Publication WO 97/13884 discloses a composite coating of a metal and an oxide of the metal wherein the oxide has a lower oxygen content than any of the metal""s oxide forms, the metal being selected from Ni, Cu, Mo, Fe or an alloy thereof. German Patent DE 195 48 718 Cl discloses the use of a solid film lubricant comprised of a metal oxide coating wherein the metal is Ti, Al, Mo, V or Cr.
U.S. Pat. No. 4,392,463 discloses a diesel engine having a first lubrication system, containing conventional engine oil, used to lubricate that section of the engine subjected to excessive wear-the valve train including the cam shaft, valve lifters, rocker arm, valve stems, etc., and a second lubricant system, utilizing diesel fuel, for lubricating the remaining section of the engine-the crankshaft and associated parts, pistons, connecting rods, etc. By being exposed to crankcase blowby exhaust gases, diesel fuel used to lubricate the crankshaft, etc. absorbs pollutants and contaminants contained therein and recirculates these contaminants through the fuel system to be burned and exhausted. By constantly being lubricated with fresh lubricant, wear on these specific parts is reduced. The reference indicates that frequent lubrication changes have been eliminated because the diesel fuel/lubricant is continuously changed and circulated through the fuel system. Since the engine oil and the first lubrication system is not exposed to crankcase blowby exhausted gases, its useful life is prolonged, thus reducing the frequency of required oil changes.
This invention relates to a method of operating an internal combustion engine comprising a valve train, said method comprising:
(A) operating said engine using a normally liquid or gaseous fuel;
(B) lubricating components of said valve train using a solid film lubricant; and
(C) lubricating said engine, including said components of said valve train, using a low-phosphorus or phosphorus-free lubricating oil composition, said low-phosphorus or phosphorus-free lubricating oil composition optionally containing an extreme-pressure additive comprised of metal and phosphorus, provided the amount of phosphorus contributed to said low-phosphorus or phosphorus-free lubricating oil composition by said extreme-pressure additive does not exceed about 0.08% by weight based on the weight of said low-phosphorus or phosphorus-free lubricating oil composition.
In one embodiment, the inventive method further comprises the following additional steps:
(D) removing part of said low-phosphorus or phosphorus-free lubricating oil composition from said engine, said removed part of said low-phosphorus or phosphorus-free lubricating oil composition (i) being combined with said fuel and consumed with said fuel as said engine is operated or (ii) being combined with the exhaust gas from said engine and removed from said engine with said exhaust gas; and
(E) adding an additional amount of said low-phosphorus or phosphorus-free lubricating oil composition to said engine to replace said removed part of said low-phosphorus or phosphorus-free lubricating oil composition.